U.S. patent application number 12/562297 was filed with the patent office on 2010-03-25 for projector apparatus using pulse-driven light sources of different colors.
This patent application is currently assigned to Casio Computer Co., Ltd.. Invention is credited to Mamoru SHIBASAKI.
Application Number | 20100073639 12/562297 |
Document ID | / |
Family ID | 42037301 |
Filed Date | 2010-03-25 |
United States Patent
Application |
20100073639 |
Kind Code |
A1 |
SHIBASAKI; Mamoru |
March 25, 2010 |
PROJECTOR APPARATUS USING PULSE-DRIVEN LIGHT SOURCES OF DIFFERENT
COLORS
Abstract
A projector apparatus comprises a light source configured to
emit light beams of a plurality of color components, emissions of
the light beams controlled individually, a projection unit
configured to form images respectively corresponding to the color
components using the light beams from the light source for each
frame and to sequentially project the images, a driving unit
configured to drive the light source so that the light beams are
emitted as light pulses having respectively predetermined pulse
widths for a period in which the projection unit projects each of
the images, a detector configured to detect deterioration levels of
the light source respectively for the color components, and a
controller configured to control the pulse widths of the light
beams emitted from the light source based on the deterioration
levels.
Inventors: |
SHIBASAKI; Mamoru;
(Tachikawa-shi, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
220 Fifth Avenue, 16TH Floor
NEW YORK
NY
10001-7708
US
|
Assignee: |
Casio Computer Co., Ltd.
Tokyo
JP
|
Family ID: |
42037301 |
Appl. No.: |
12/562297 |
Filed: |
September 18, 2009 |
Current U.S.
Class: |
353/31 |
Current CPC
Class: |
H04N 9/3194 20130101;
H05B 31/50 20130101; G03B 33/08 20130101; H04N 9/3155 20130101;
H04N 9/3158 20130101; H05B 45/20 20200101; H04N 9/3111 20130101;
H05B 45/22 20200101 |
Class at
Publication: |
353/31 |
International
Class: |
G09G 5/02 20060101
G09G005/02; G03B 21/14 20060101 G03B021/14 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 25, 2008 |
JP |
2008-245247 |
Claims
1. A projector apparatus comprising: a light source configured to
emit light beams of a plurality of color components, emissions of
the light beams controlled individually; a projection unit
configured to form images respectively corresponding to the color
components using the light beams from the light source for each
frame and to sequentially project the images; a driving unit
configured to drive the light source so that the light beams are
emitted as light pulses having respectively predetermined pulse
widths for a period in which the projection unit projects each of
the images; a detector configured to detect deterioration levels of
the light source respectively for the color components; and a
controller configured to control the pulse widths of the light
beams emitted from the light source based on the deterioration
levels.
2. The projector apparatus according to claim 1, wherein the light
source includes light-emitting diodes configured to emit light of
red, green and blue.
3. The projector apparatus according to claim 1, wherein the
controller comprises a storage unit configured to store control
information for the pulse widths in association with the
deterioration levels of the light source respectively for the color
components.
4. The projector apparatus according to claim 1, wherein the
controller is configured to control the pulse widths so that total
chromaticity of the light beams emitted from the light source are
balanced in one frame.
5. The projector apparatus according to claim 1, wherein the
driving unit pulse-drives the light source to present predetermined
number of gradations of the colors.
6. The projector apparatus according to claim 1 further comprising
a display unit configured to form an optical image in gradations
using the light beams of the color components emitted from the
light source, and wherein the display unit reproduces the
predetermined number of gradations at a maximum.
7. The projector apparatus according to claim 1, wherein the
detector is configured to detect the deterioration levels of the
light source at predetermined intervals.
8. The projector apparatus according to claim 1, wherein the
detector comprises a measurement unit configured to measure
illumination values for each of the color components.
9. The projector apparatus according to claim 8, wherein the
controller comprises: a determination unit configured to determine
whether or not each of the illumination values is smaller than a
predetermined illumination value; a changing unit configured to
drive the light source to narrow a pulse width of a color component
corresponding to an illumination value larger than the
predetermined illumination value when the determination unit
determines that an illumination value of one of the color
components is lower than the predetermined illumination value.
10. The projector apparatus according to claim 9, wherein, when the
determination unit determines that illumination values of a
plurality of color components are smaller than the predetermined
illumination value, the changing unit narrows pulse widths of the
color components excepting a color component corresponding to a
smallest illumination value.
11. The projector apparatus according to claim 9, wherein the
changing unit is configured to narrow the pulse width of the color
component corresponding to the illumination value larger than the
predetermined illumination value so that total chromaticity of the
light beams emitted from the light source are balanced in one
frame.
12. A control program for use with a projector apparatus comprising
a light source configured to emit light beams of a plurality of
color components, emissions of the light beams controlled
individually, the control program comprising; first computer
readable program means for forming images respectively
corresponding to the color components using the light beams from
the light source for each frame and sequentially projecting the
images; second computer readable program means for driving the
light source so that the light beams are emitted as light pulses
having respectively predetermined pulse widths for a period in
which each of the images are projected; third computer readable
program means for detecting deterioration levels of the light
source respectively for the color components; and forth computer
readable program means for controlling the pulse widths of the
light beams emitted from the light source based on the
deterioration levels.
13. A control method for a projector apparatus comprising a light
source configured to emit light beams of a plurality of color
components, emissions of the light beams controlled individually,
the method comprising: forming images respectively corresponding to
the color components using the light beams from the light source
for each frame and sequentially projecting the images; driving the
light source so that the light beams are emitted as light pulses
having respectively predetermined pulse widths for a period in
which each of the images is projected; detecting deterioration
levels of the light source respectively for the color components;
and controlling the pulse widths of the light beams emitted from
the light source based on the deterioration levels.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2008-245247,
filed Sep. 25, 2008, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF TEE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a projector apparatus, a
control program for the projector apparatus and a light source
controlling method for the projector apparatus. The projector
apparatus uses light sources which emit light beams of different
colors to project an image.
[0004] 2. Description of the Related Art
[0005] Conventionally, a projector apparatus having a halogen lamp
light source has been used in general. In recent years, a projector
apparatus which employs, as light sources, three LEDs respectively
emitting red, green and blue light beams has been proposed to
downsize the apparatus and to make the apparatus portable. However,
the projector apparatus which uses the three LEDs cannot project an
image with a higher luminance. This is because the LEDs emit light
beams by turns, and in each moment, only one of the red, green and
blue LEDs is emitting a light beam. In addition, luminance of an
LED is lower than that of a halogen lamp.
[0006] Jpn. Pat. Appln. KOKAI Publication No. 2004-317558 discloses
a projector which can project an image with a higher luminance.
According to the projector, when a light beam of one color is
emitted from an LED, the other LEDs are driven by low power to emit
light beams For example, while an LED is emitting a red light beam,
the other LEDs are driven by low power and emit green and blue
light beams. Thus, an image can be projected with a higher
luminance.
[0007] However, an LED has characteristics that a color of the
emitted light beam varies with a value of the drive current when
the driving current is lower than the rated current for the LED.
That is, when an LED is driven by low drive current to emit a light
beam, the color of the light beam differs from the original
emission color of the LED.
[0008] Therefore, when the red LED emits the red light beam and the
green and blue LEDS are driven by the low power to emit the green
and blue light beams, a total emission color from the projector
differs from a combination of a large amount of red, a little
amount of green and a little blue. The total emission color
includes colors which are varied from green and blue due to the low
power driving in addition to red and presents an unexpected
color.
[0009] Moreover, an LED deteriorates as the LED is used longer (as
emitting time becomes longer). Therefore, with the deterioration,
the luminance of the LED is decreased and chromaticity may also be
varied. Thus, the above projector, in which while one LED (red, for
example) is emitting a light beam, the other LEDs (green and blue)
are also driven, deteriorates more quickly than a projector in
which only one of the LEDs emits a light beam at a time. As a
result, the total emission color of the projector may include
colors which are varied from green and blue due to the
deterioration in addition to red and presents an unexpected
color.
[0010] Therefore, according to Jpn. Pat. Appln. KOKAI Publication
No. 2004-317558, although an image can be projected with a higher
luminance, chromaticity adjustment for the projected image is
impossible.
BRIEF SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to provide a
projector apparatus, a control program for the projector apparatus
and a light source controlling method for the projector apparatus
which can project an image with a higher luminance and adjust
chromaticity of the image.
[0012] According to an embodiment of the present invention, a
projector apparatus comprises:
[0013] a light source configured to emit light beams of a plurality
of color components, emissions of the light beams controlled
individually;
[0014] a projection unit configured to form images respectively
corresponding to the color components using the light beams from
the light source for each frame and to sequentially project the
images;
[0015] a driving unit configured to drive the light source so that
the light beams are emitted as light pulses having respectively
predetermined pulse widths for a period in which the projection
unit projects each of the images;
[0016] a detector configured to detect deterioration levels of the
light source respectively for the color components; and
[0017] a controller configured to control the pulse widths of the
light beams emitted from the light source based on the
deterioration levels.
[0018] According to another embodiment of the present invention, a
control program for use with a projector apparatus comprising a
light source configured to emit light beams of a plurality of color
components, emissions of the light beams controlled individually,
the control program comprises;
[0019] first computer readable program means for forming images
respectively corresponding to the color components using the light
beams from the light source for each frame and sequentially
projecting the images;
[0020] second computer readable program means for driving the light
source so that the light beams are emitted as light pulses having
respectively predetermined pulse widths for a period in which each
of the images are projected;
[0021] third computer readable program means for detecting
deterioration levels of the light source respectively for the color
components; and
[0022] forth computer readable program means for controlling the
pulse widths of the light beams emitted from the light source based
on the deterioration levels.
[0023] According to another embodiment of the present invention, a
control method for a projector apparatus comprising a light source
configured to emit light beams of a plurality of color components,
emissions of the light beams controlled individually, the method
comprises:
[0024] forming images respectively corresponding to the color
components using the light beams from the light source for each
frame and sequentially projecting the images;
[0025] driving the light source so that the light beams are emitted
as light pulses having respectively predetermined pulse widths for
a period in which each of the images is projected;
[0026] detecting deterioration levels of the light source
respectively for the color components; and
[0027] controlling the pulse widths of the light beams emitted from
the light source based on the deterioration levels.
[0028] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages f the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0029] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the present invention and, together with the general description
given above and the detailed description of the embodiments given
below, serve to explain the principles of the present invention in
which:
[0030] FIG. 1 is a block diagram showing a circuit configuration of
a projector apparatus according to an embodiment of the present
invention;
[0031] FIG. 2 is a schematic view showing an example of an initial
emission pattern for LEDs according to the embodiment;
[0032] FIG. 3 shows schematically a pulse-width control table
according to the embodiment;
[0033] FIG. 4 is a flowchart of pulse emissions according to the
embodiment; and
[0034] FIG. 5 is schematic view showing an example of a pulse-width
pattern of emissions in the case where a frame is divided into
four.
DETAILED DESCRIPTION OF THE INVENTION
[0035] Hereinafter, an embodiment of the present invention will be
described with reference to the accompanying drawings. Some
limitations may be set on the embodiment for a technical reason;
however, a scope of the invention will not be limited to the
embodiment and the drawings described hereinafter.
[0036] An explanation will be given on one embodiment of the
invention referring to the drawings.
[0037] FIG. 1 is a block diagram showing an electronic
configuration of a projector apparatus 1 according to an
embodiment. The projector apparatus 1 includes a controller 11, an
input-output (I/O) interface 12, an image converter 13, a display
encoder 14, and a display driver 15. In addition, the projector
apparatus 1 includes input-output (I/O) connector unit 16 and a
system bus 17. An image signal (or image data) complying with one
of the various standards is input to the I/O connector unit 16, and
the image signal is sent to the image converter 13 via the I/O
interface 12 and the system bus 17. The image converter 13 converts
the image signal into a predetermined format which is appropriate
to be displayed and the converted image signal is sent to the
display encoder 14.
[0038] The display encoder 14 extracts the image signal and stores
the image signal in a video RAM 18. The display encoder 14
generates a video signal from the data stored in the video RAM 18
and outputs the generated video signal to the display driver
15.
[0039] The display driver 15 receives the video signal from the
display encoder 14 and drives a digital micromirror device (DMD)
19, which functions as a display element, based on the video signal
at an appropriate frame rate to achieve resolution of 256
gradations. A light-source optical system includes a light source
unit 20. Light beams emitted from the light source unit 20 strike
the DMD 19 and are reflected by the DMD 19 to form an optical
image. The optical image is projected on a screen (not shown)
through movable lenses 21 of a projection optical system. The lens
motor 22 drives the lenses 21 to adjust focusing and zooming.
[0040] An image compress/decompress unit 23 performs adaptive
discrete cosine transformation (ADCT) and Huffman coding processing
on a luminance signal and a color difference signal in the image
signal to compress the image data. The compressed image data is
written into a memory card 24 or a removable storage medium.
Moreover, the image compress/decompress unit 23 reads out the image
data stored in the memory card 24 and decompresses or expands items
of the image data, which collectively form a moving image, in units
of frame. The expanded image data are sent to the display encoder
14 via the image converter 13. Thus, images such as a moving image
can be displayed based on the image data stored in the memory card
24.
[0041] The controller 11 includes a CPU (not shown), peripheral
circuitry of the CPU, a ROM 111 and a RAM 112. The controller 11
controls operations of units in the projector apparatus 1. The ROM
111 prestores programs for various settings in the projector
apparatus 1, a program represented by a flowchart to be described
below, and various data which the CPU utilizes. The RAM 112
functions as a work memory.
[0042] A key/indicator device 25 includes a main key and indicators
provided, for example, on a main body (not shown) of the projector
apparatus 1. An operation signal generated by the key/indicator
device 25 is transmitted to the controller 11. An infrared (Ir)
receiver 26 receives a key operation signal sent from a remote
controller (not shown). An infrared (Ir) processor 27 demodulates
the received key operation signal and sends the demodulated signal
as a code signal to the controller 11.
[0043] The system bus 17 connects the controller 11 with an audio
processor 30. The audio processor 30 includes an audio source
circuit such as a PPM audio source. The audio processor 30 converts
audio data into an analog signal and drives a speaker 31 to output
the audio signal when a projection mode or a reproduction mode is
set.
[0044] The light source unit 20 includes a red-color LED 20R which
emits red light, a green-color LED 20G which emits green light and
a blue-color LED 20B which emits blue light. The controller 11
controls a light source controller 32 based on an image signal to
cause the LEDs 20R, 20C and 20B to emit light time-divisionally and
to be pulse-driven.
[0045] Illuminance sensors 335, 33G and 33B are provided near the
corresponding red-color LED 20R, green-color LED 20G, and
blue-color LED 20B. The illuminance sensors 33R, 33G and 33B detect
illuminance of the corresponding LEDs 20R, 20G and 20B. The
detected illuminance values of the LEDs 20R, 20G and 20B are
supplied to the controller 11 via a transfer circuit (not
shown).
[0046] The ROM 111 stores an initial emission pattern PP
illustrated in FIG. 2, which shows initial pulse widths contained
in one frame. In normal driving, full-emissions of the LEDs 20R,
20G and 20B divide one frame equally (time-division emission).
Hereinafter, "full-emission" or "time-division emission" of an LED
will mean that the LED emits a light beam pulse having a width
which matches a given. period of time (one third of one frame in
FIG. 2) to divides the one frame. The pattern PP also includes
pulse-emission widths other than the time-division emission pulse
width. When one LED is in the time-division emission, the other
LEDs emit light beam pulses at certain intervals. In the pattern PP
shown in FIG. 2, time-division emissions of the LEDs 20R, 20G and
20B divide equally the frame; however, the embodiment is not so
limited. For example, the time-division emission pulse width of the
LED 20G may be longer than time-division emission pulse widths of
the other LEDs to emit light with a higher luminance.
[0047] The more frequently an LED is pulse-driven to emit a light
beam, the more appropriate chromaticity can be provided when the
DMD forms the projection image. In the present embodiment, an LED
is pulse-driven 256 times per given period in correspondence with
the 256 (0-255) gradations.
[0048] As an LED emits a light beam more frequently and with
shorter pulse width to make a light amount a predetermined value,
the chromaticity can be balanced more appropriately. Furthermore,
the display element of the present embodiment, the DMD 19, forms an
image reflecting the light coming from the light source unit 20 to
present resolution of 256 gradations. Therefore, pulse-driving of
the LEDs synchronized with the reflection by the DMD 19 (256
gradations) allows chromaticity of color combination resulting from
the emissions of the LEDs being appropriately balanced.
[0049] Therefore, according to the initial emission pattern PP,
while the LED 20R is in time-division emission, the LEDs 20G and
20B are pulse-driven to emit pulsed light beams for 256 gradations.
As shown in FIG. 2, the pulse width of the LED 20G emission is
narrower than the pulse width of the LED 20B emission, in the
present embodiment.
[0050] Similarly, while the LED 20G is in time-division emission,
the LEDs 20R and 20B are pulse-driven to emit pulsed light beams
for 256 gradations. The pulse width of the LED 20R emission is
narrower than the pulse width of the LED 20B emission as shown in
FIG. 2.
[0051] While the LED 20B is in time-division emission, the LEDs 20R
and 20G are pulse-driven to emit pulsed light beams for 256
gradations. The pulse width of the LED 20R emission is wider than
the pulse width of the LED 20G emission in FIG. 2.
[0052] The pulse width of the LED 20G for the case when the LED 20R
or 20B is in time-division emission is narrower than the pulse
width of the LED 20B for the case when the LED 20R or 20G is in
time-division emission.
[0053] The pulse width of the LED 20R for the case when the LED 20G
is in the time-division emission is narrower than the pulse width
for the case when the LED 20B is in time-division emission. The
pulse width of the LED 20R for the case when the LED 20G is in the
time-division emission may be equal to the pulse width of the LED
20G for the case when the LED 20R or 20B is in the time-division
emission. The pulse width of the LED 20R for the case when the LED
20G is in time-division emission may be equal to the pulse width of
the LED 20G for the case when the LED 20R or 20B is in
time-division emission.
[0054] The pulse widths shown in the initial pattern. PP are
determined to increase luminance to some extent and to hardly
affect chromaticity.
[0055] The ROM 111 stores pulse-width control table PT shown in
FIG. 3. The control table PT stores pulse-width controlling
information which is set depending on conditions. The conditions
can he designated depending on whether "R illuminance" is smaller
than a predetermined illuminance value (YES) or not (NO), whether
"C illuminance" is smaller than the predetermined illuminance value
(YES) or not (NO), and whether "B illuminance" is smaller than the
predetermined illuminance value (YES) or not (NO). The control
table PT stores pulse width control information. ("no change" and
"narrow pulse width") for the LEDs 20R, 20G and 20B in association
with the respective conditions for each of the "R full-emission",
"G full-emission" and "B full-emission". When the "R full-emission"
is set, the LED 20R is in time-division emission. When the "G
full-emission" is set, the LED 20G is in time-division emission.
Further, when the "B full-emission" is set, the LED 20B is in
time-division emission.
[0056] As shown in FIG. 3, in the condition (1) where all the
illuminance values of R, G and B are equal to or larger than the
predetermined illuminance value (NO for all colors) and in
condition (8) where all illuminance values of R, G and B are
smaller than the predetermined illuminance value (YES for all
colors), pulse widths are not changed when even any of "R
full-emission", "G full-emission" and "B full-emission" is set.
Adjustment of the entire chromaticity in one frame is required when
deterioration is generated in one or two of the three LEDs. Thus,
in the condition (1) or (8), since variations in the illuminance
values are small enough or within tolerance, it is not required to
adjust entire chromaticity. However, in condition (2) where the
illuminance value of the LED 20B is smaller than the predetermined
illuminance value, pulse widths of the LEDs 20R and 20G other than
the LED 20B are narrowed. That is, according to the control table
PT, when illuminance of one or two of the LEDs become smaller than
the predetermined illuminance value, pulse width(s) of the other
LED(s) having illuminance value(s) equal to or larger than the
predetermined illuminance value is narrowed. Accordingly, entire
chromaticity in one frame can be adjusted.
[0057] By means of the above-described configuration, the
controller 11 of the projector apparatus 1 executes the processing
expressed in the flowchart shown in FIG. 4 based on a program
stored in the ROM 111 at given intervals.
[0058] The controller 11 reads the initial emission pattern PP from
the ROM 111 and sets the read initial pulse widths contained in the
initial emission pattern PP to a given area in the RAM 112 (step
SA1). The controller 11 starts time measurement with a timer T
which is provided in the controller 11 (step SA2).
[0059] The controller 11 determines whether or not the time
measured by the timer T arrives at or exceeds a predetermined time
(step SA3). When the time measured by the timer T is shorter than
the predetermined time (No in step SA3), the flow goes to step SA8
without executing steps SA4 to SA7. The controller 11 causes
pulse-driving of the LEDs 20R, 20G and 20B based on pulse widths
which are already set and projects an image (step SA8).
[0060] If processing of step SA6 has not been executed (if none of
the LEDs has deteriorated), the LEDs are driven in step SA6 based
on the initial pulse widths set in step SA1. The initial emission
pattern PP which presents the initial pulse widths can provide
enough luminance for the image and achieve 256 gradations in order
not to affect the chromaticity.
[0061] Consequently, when the LEDs have not deteriorated and the
processing of step SA6 has not been executed, the initial emission
pattern PP provides the projected image with higher luminance. In
addition, pulsed emissions of the LEDs 20R, 20G and 20B based on
the initial emission pattern PP do not cause change in the
chromaticity due to change in the currents. Therefore, the pulsed
emissions of the LEDs 20R, 20G and 20B based on the initial
emission pattern PP do not cause change in the total chromaticity
in one frame and present an appropriate projection image.
[0062] In addition, the pulse widths in the initial emission
pattern PP are defined not to make chromaticity change and to
obtain appropriate light amount.
[0063] When it is determined that the time measured by the timer T
arrives at or exceeds the predetermined time (Yes in step SA3), the
controller 11 drives the illuminance sensors 33R, 33G and 33B to
measure illuminance values of the LEDs 22R, 22G and 22B (step SA4).
The controller 11 determines whether or not any of the measured
illuminance values of the LEDs 22R, 22G and 22B in smaller than the
predetermined illuminance value (step SA5).
[0064] If an LED is used longer, the LED deteriorates and the
deterioration decreases an illuminance (luminance) value of the
LED. In the present embodiment, total emission periods of the LEDs
are not equal in one frame, as shown in the initial emission
pattern PP of FIG. 2. Specifically, the total emission period of
the LED 20B is the longest and the total emission period of the LED
20G is the shortest. This difference in the total emission periods
generates difference in the illuminance values of the LEDs 20R, 20G
and 20B. If the projector apparatus 1 is used much longer, the
difference in the illuminance values grows significantly larger. As
a result, the illuminance values of the LEDs 20R, 20G and 20B may
be decreased. below the predetermined illuminance value.
[0065] When an illuminance value of any of the LEDs is decreased
below the predetermined illuminance value (Yes in step SA5), pulse
widths of the other LEDs, which have illumination values equal to
or larger than the predetermined illuminance value, are adjusted
based on the condition of the illuminance values (step SA6). The
adjustment in step SA6 is executed based on the pulse-width control
table PT shown in FIG. 3.
[0066] Thus, adjustment of the pulse widths can be performed with
simple processing by referring to the control table PT which is
previously stored.
[0067] For example, as the LEDs keep emitting light beams having
the pulse widths shown in FIG. 2 and the LED 20B is used most
frequently, the illuminance value of the LED 20B may be decreased
below the predetermined illuminance value as denoted by condition
(2) in FIG. 3. In such a case the determination result in step SA5
becomes "Yes", and the pulse widths of the LEDs 20R and 20G are set
narrower in step SA6. Alternatively, when the illuminance values of
the LED 20G and 20B are decreased below the predetermined
illuminance value as denoted by condition (4) in FIG. 3, the pulse
width of the TED 20R that is other than the LEDs 20G and 20B is
narrowed.
[0068] The controller 11 narrows a pulse width of an LED keeping an
illuminance value equal to or larger than the predetermined
illuminance value without deterioration. By reducing the
illuminance value of the LED keeping enough illuminance, the
illuminance values of the LEDs are balanced. As a result, the total
chromaticity of the projection light emitted from the LEDs 20R, 20G
and 20B can be prevented from having unexpected chromaticity.
[0069] Then, the controller 11 resets the timer T (step SA7) and
executes step SA8. In step SA8, as described, the LEDs 20R, 20G and
20B are driven to emit light beams at the pulse widths set in step
SA6.
[0070] As described above, pulse emissions of the LEDs at the pulse
widths initially set in step SA1 increase illuminance in normal
driving. The emission is controlled merely by switching on/off of
the LEDs and it is not required to change currents applied to the
LEDs. Therefore, chromaticity change is not generated by the change
in the currents. When an illuminance value of any of the LEDs is
decreased below the predetermined illuminance value, the pulse
widths of the other LEDs having luminance values equal to or larger
than the predetermined illuminance value are adjusted to be
narrowed without changing the currents applied to the LEDs.
Therefore, unexpected chromaticity change is not generated by the
change in the currents.
[0071] In the projector apparatus 1 according to the present
embodiment, chromaticity of the projected image is adjusted easily,
since unexpected color change in the emission colors of the LEDs
20R, 20G and 20B due to the change in the currents is not
generated. Therefore, when the illuminance values of the LEDs are
reduced, high luminance can be provided for the projected image
avoiding complicated chromaticity adjustment.
[0072] In the present embodiment, the processing of step SA4 is
executed every predetermined period T. Therefore, measurement of
the illuminance values of the LEDs can be performed timely. In the
above embodiment, it is assumed that decrease in an illuminance
value of an LED is brought about mainly by deterioration in the
LED. However, in actuality, variation in the illuminance value may
be produced due to environmental temperature and individual
difference of the LED. In the present embodiment, to address such
variation in the illuminance, the actual luminance values of the
LEDs are periodically measured by the illuminance sensors and it is
checked whether an illuminance value of any of the LEDs becomes
lower than the predetermined illuminance value. Thus, the variation
in the luminance value of the LED resulting from various factors
can be detected properly.
[0073] The time interval T at which the illuminance sensors 33R,
33G and 335 measure the illuminance values of the LEDs in step SA4
may be defined based on when the LEDs are mounted, the initial
pulse widths of the LEDs, or usage environment of the projector
apparatus 1.
[0074] In the present embodiment, the processing of step SA4 is
executed at given intervals T; however, the invention is not so
limited. The processing may be executed automatically at the time
of starting up the projector apparatus 1, or may be executed in
response to an instruction made by the user.
[0075] The projector apparatus 1 of the present embodiment includes
three illumination sensors 33R, 33G and 33B in accordance with the
three LEDs 20R, 20G and 20B. However, such configuration is
possible that a single illumination sensor is provided and the
illumination sensor measures the illuminance values of the LEDs
20R, 20G and 20B in synchronism with time-division emissions of the
LEDs.
[0076] In the projector apparatus 1 of the present embodiment, the
illuminance sensors are provided near the corresponding LEDs and
directly measure the light beams emitted from the LEDs. However,
the illuminance sensors may measure light reflected by the DMD 19
as unnecessary light which will not be used to form a projection
image. According to the projector apparatus 1 described herein,
regardless of arrangement of the illumination sensors, proper
illumination values of the LEDs can be measured in the case where
the illumination values are decreased due to external factors as
well as the aged deterioration of the LEDs.
[0077] In the projection apparatus 1 of the present embodiment, the
time-division emissions of the LEDs 20R, 20G and 20B divide one
frame into three periods. However, as shown in FIG. 5, one frame
may be divided into four periods. In this case, fourth period of
divided frame is assigned to white light emission. In the period of
the white light emission, the LEDs 20R, 20G and 20B are
pulse-driven for 256 gradations at pulse widths preliminary defined
as initial values. When an illumination value of any of the LEDs
becomes lower than the predetermined illumination value, the pulse
widths of the other LEDs keeping illumination values equal to or
larger than the predetermined illumination value are adjusted to be
narrowed based on the control table PT shown in FIG. 3.
[0078] In the white light emission period, if no LED presents a
lower illumination value than the predetermined illumination value,
the highest luminance can be derived by causing the LEDs 20R, 20G
and 20B fully emitted without chromaticity change. On the other
hand, the chromaticity of the white light can be adjusted arbitrary
by pulse-driving the LEDs.
[0079] In the present embodiment, the LEDs are pulse-driven to emit
256 light pulses per period. However, the LEDs may be pulse-driven
more frequently, or alternatively, the pulse-emission frequency may
be lowered. In any case, each LED is set to emit light pulses at
constant intervals in an emission period. By changes pulse widths
of the LEDs, the chromaticity can be adjusted. Since the currents
to be applied to the LEDs are not changed, the chromaticity change
cannot be generated.
[0080] According to the present embodiment, the initial emission
pattern PP includes the pulse widths which hardly affect the entire
chromaticity in one frame; however, the invention is not so
limited. For example, the projector apparatus 1 may be configured
to have a plurality of operating modes including a luminance
preceding mode, a normal operating mode, and a chromaticity
preceding mode, which are settable based on an arbitrary selection
made by the user. The pulse widths may be set longer, normally or
shorter in the luminance preceding mode, normal operating mode, or
the chromaticity preceding mode.
[0081] In the present embodiment, when an illuminance value of an
LED becomes smaller than the predetermined illuminance value, the
processing of step SA6 is executed. When illuminance values of more
than one LED are below the predetermined illuminance value as
denoted by conditions (4), (6), (7) and (8) in FIG. 3, the smallest
illuminance value may be made as a reference value, and pulse
widths of the other LEDs may be narrowed to present the reference
value. Thus, the chromaticity can be adjusted more precisely.
[0082] The projector apparatus 1 of the present embodiment utilizes
the LEDs having different emission colors as light sources.
However, other light sources having different emission colors such
laser light sources may be utilized.
[0083] While the description above refers to particular embodiments
of the present invention, it will be understood that many
modifications may be made without departing from the spirit
thereof. The accompanying claims are intended to cover such
modifications as would fall within the true scope and spirit of the
present invention. The presently disclosed embodiments are
therefore to be considered in all respects as illustrative and not
restrictive, the scope of the invention being indicated by the
appended claims, rather than the foregoing description, and all
changes that come within the meaning and range of equivalency of
the claims are therefore intended to be embraced therein. For
example, the present invention can also be implemented as a
computer readable recording medium in which a program for allowing
a computer to execute predetermined means, allowing the computer to
function as predetermined means, or allowing the computer to
realize a predetermined function is recorded.
* * * * *